The most important mission and ultimate goal of all research in the medical field is to understand the etiology of diseases and their treatment to reduce/eliminate disease. Determination of causality between a cause (independent variable) and a disease (dependent variable), no matter how often can be difficult, but it’s a paramount of importance. In what way can causality proceed? And what process should be taken to see that certain factors are associated with a particular disease? The following is an explanation of this issue.